Soti·Software Engineer·Onsite - System Design / Architecture
May 2026
System design round at Soti for a software engineer role, focused entirely on designing an IP firewall blacklist service. The whole session revolved around caching and read-path latency, which I wasn't fully prepared to go deep on.
- Design the API surface for an IP firewall blacklist system that supports adding, removing, updating, and querying blacklisted IPs and CIDR ranges.
- How would you store exact IP addresses alongside CIDR ranges in the backend, and what data structures or storage systems would you use?
- How would you design the read path for blacklist checks to achieve very low latency at high throughput?
- Walk through how cache invalidation and update propagation would work when the blacklist changes.
- How would you handle scale, consistency tradeoffs, failure scenarios, and observability for this system?
“Started with the obvious CRUD endpoints and felt okay about it until they asked how I'd handle CIDR ranges differently from exact IPs in the API contract.”